Hitherto, as a device for dispensing a very small amount of a liquid drug such as antibiotics and a carcinostatic substance to a blood vessel, urinary bladder and the like, there is proposed an infusor of a liquid drug with a bladder (e.g. Japanese Unexamined Patent Publication No. 11465/1987) wherein the liquid drug is charged into the bladder made of elastic material and the liquid drug is dispensed into a blood vessel and the like for a relatively long period of time with the use of a shrinkage force of the bladder. The infusor described in the above publication has a constitution as shown in prior art FIG. 17. The liquid drug injected from an inlet portion 352 wherein a check valve 351 is mounted, is charged into a bladder 356 through an inlet port 354 made on a tubular body 353. In that case, an end portion of a tube 357 remaining within a blood vessel is stopped up with a hand, or a flow control valve 358 is throttled at its maximum, in order to prevent a flow-out of the liquid drug. After being charged in the bladder in a predetermined amount, the liquid drug is dispensed to the blood vessel by the shrinkage force of the bladder 356 through an outlet port 359, an outlet portion 360 and the tube 357. The publication describes that the above-mentioned infusor has a simpler structure than liquid-transfusing pumps and the like used before proposal of the infusor, and make the treatment thereof easy.
The infusor, however, has a problem in which fine flow regulation of liquid drug is difficult because the amount of liquid drug is effected by the sectional area of the outlet port 359, the throttle ratio of the flow control valve 358, the resistance of the pipe line of a catheter for the blood vessel connected to the infusor, and the like. Further, a considerable amount of the liquid drug remains within the tubular body 353 and the like without being dispensed to the human body, since the bladder 356 can deform only in a radial direction of the tubular body 353 (such a direction shown by X in FIG. 17).
U.S. Pat. No. 4,318,400 discloses a medical infusor having an elastomeric bladder in a housing wherein a piston mounted in the housing slides along an axis of the housing while contacting to an inner surface of the housing with the dispensation of the liquid drug in the bladder.
However, two shafts in the bladder are at both ends of the bladder when the liquid drug is charged therein, that is to say, two shafts are not interconnected, so that the bladder inflating into a cylindrical form is not supported in an axial direction of the housing. Therefore, a part of the bladder becomes bulb-shaped whereby generating a sudden rise of pressure in the bladder. Thus, the liquid drug in the bladder cannot be dispensed at a constant flow velocity.
Accordingly, it is an object of the present invention to provide a liquid infusion device capable of finely regulating the flow rate of the liquid drug, dispensing the liquid drug at a substantially constant flow velocity, and reducing the residual amounts of liquid drug in the bladder.